Fuel slurry preparation system and method

ABSTRACT

A system includes a grinder, a storage unit, and an organic compound production unit. The grinder is configured to produce a fuel slurry from a solid fuel, a liquid, and an organic compound that is miscible with the liquid. The storage unit is configured to supply the organic compound to the grinder. The organic compound production unit is configured to receive a portion of syngas generated by a gasifier to generate the organic compound for supply to the storage unit.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to the preparation of fuel slurries used in gasification processes, and more specifically to enhancing efficiency of the fuel slurry preparation.

Synthesis gas or “syngas” is a mixture of carbon monoxide (CO) and hydrogen (H₂). Other gaseous components, such as carbon dioxide (CO₂), may also be present in syngas streams in lesser degrees. Syngas may be used in a number of processes, such as in power generation, steam generation, heat generation, substitute natural gas (SNG) production, as well as chemical synthesis. Syngas can be produced using gasification processes, which utilize a solid, liquid, and/or gaseous carbonaceous fuel source to react with oxygen (O₂) to produce the syngas within a gasifier. While certain carbonaceous fuels may be provided to the gasifier directly, in some situations, solid carbonaceous fuel sources may be provided to the gasifier as a fuel slurry, where the solid fuel is dispersed within a liquid, such as water. The liquid is used to facilitate flow of the solid fuel into the gasifier as well as to facilitate dispersal of the solid fuel within the gasifier, for example to increase gasification efficiency. The liquid is generally mixed with the solid fuel in a grinder and/or mixing vessel to prepare the fuel slurry.

BRIEF DESCRIPTION OF THE INVENTION

Certain embodiments commensurate in scope with the originally claimed disclosure are summarized below. These embodiments are not intended to limit the scope of the claimed disclosure, but rather these embodiments are intended only to provide a brief summary of possible forms of the disclosure. Indeed, the disclosure may encompass a variety of forms that may be similar to or different from the embodiments set forth below.

In a first embodiment, a system includes a grinder, a storage unit, and an organic compound production unit. The grinder is configured to produce a fuel slurry from a solid fuel, a liquid, and an organic compound that is miscible with the liquid. The storage unit is configured to supply the organic compound to the grinder. The organic compound production unit is configured to receive a portion of syngas generated by a gasifier to generate the organic compound for supply to the storage unit.

In a second embodiment, a method includes providing an organic compound from a storage unit to a grinder. The method also includes mixing the organic compound with a solid fuel and a liquid to generate a fuel slurry via the grinder. In addition, the method includes generating an additional amount of the organic compound from a syngas, wherein the syngas is generated from the fuel slurry via a gasifier. Further, the method includes providing the additional amount of the organic compound to the grinder for mixing the fuel slurry or to the storage unit.

In a third embodiment, a system includes a controller. The controller is configured to monitor a solids concentration of a fuel slurry comprising a mixture of a solid fuel, an organic compound, and a liquid, and to control an amount of the organic compound supplied to the mixture based on the monitored solids concentration. The organic compound is at least partially recycled from a syngas generated from the fuel slurry via a gasifier.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 is a block diagram illustrating an embodiment of a slurry preparation system configured to prepare a fuel slurry for gasification;

FIG. 2 is a block diagram illustrating an embodiment of the slurry preparation system of FIG. 1 having a storage unit configured to supply an organic compound to a grinder for slurry preparation;

FIG. 3 is a block diagram illustrating an embodiment of the grinder of FIG. 2 having one or more grinding and mixing stages for slurry preparation;

FIG. 4 is a block diagram illustrating an embodiment of the slurry preparation system of FIG. 2 coupled to multiple gasifiers configured to generate syngas for eventual production of an organic compound used for slurry preparation;

FIG. 5 is a process flow diagram illustrating an embodiment of a method for generating a fuel slurry using an organic compound or mixture of organic compounds;

FIG. 6 is a process flow diagram illustrating an embodiment of a method for controlling a fuel slurry preparation system;

FIG. 7 is a process flow diagram illustrating an embodiment of a method for performing the control step of FIG. 6; and

FIG. 8 is a process flow diagram illustrating an embodiment of a method for controlling a fuel slurry preparation system during and after gasifier operation.

DETAILED DESCRIPTION OF THE INVENTION

One or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

Present embodiments of the disclosure are directed toward systems and methods for preparing a fuel slurry for gasification by mixing a solid fuel (e.g., coal, biomass) with a liquid (e.g., water) and an organic compound (e.g., an alcohol). An additional portion of the organic compound may, in some embodiments, be generated from syngas produced via gasification. The disclosed embodiments include the additional organic compound, which may be recycled from syngas generated through the gasification process. Embodiments of the system described herein include a grinder for mixing the solid fuel, the liquid, and one or more organic compounds; one or more storage units for supplying the organic compounds to the grinder; and an organic compound production unit. A controller may be used to control flows of the organic compound and/or the liquid into the grinder in desired proportions and at prescribed times relative to one another. The controller also may maintain a supply of the organic compound in the storage unit so that, when the gasifier is restarted, the organic compound is available for mixing with or generating the fuel slurry. Such a configuration may be desirable to enable the use of the organic compound even though the organic compound is not being produced from syngas.

It should be noted that, in the following discussion, the term “organic compound” may refer to a single organic compound, or to a mixture of such compounds. For example, the organic compound may include a mixture of organic compounds having varying purity levels so that the organic compound concentration is diluted. Furthermore, it should be noted that slurry enhancers may be co-introduced with the organic compound or the liquid to further improve the desired characteristics of the slurry. Potential enhancers may include pH adjusters, particle dispersants, stabilizers towards slurry sedimentation, among others.

FIG. 1 illustrates a block diagram of an embodiment of a system 10 that prepares a fuel slurry using an organic compound to increase the solids concentration of the fuel slurry. The system 10 includes a feedstock preparation unit 12 that receives a solid fuel 14 and prepares the solid fuel 14 for mixing with a liquid 16 and an organic compound 18. The solid fuel 14 may be solid particulate and/or solid pieces of a carbonaceous feedstock, such as coal. The feedstock preparation unit 12 may include a grinder, a mill, or any similar vessel that is capable of producing smaller particles from large particles of the solid fuel 14. As illustrated, the liquid 16 and the organic compound 18 may be introduced to or otherwise mixed from the solid fuel 14 downstream of the feedstock preparation unit 12. However, in other embodiments, one or both of the liquid 16 and the organic compound 18 may be introduced directly into the feedstock preparation unit 12.

A slurry preparation unit 20 configured to receive the solid fuel 14, the liquid 16, and the organic compound 18 (e.g., as a single or separate streams) is disposed downstream from the feedstock preparation unit 12. The slurry preparation unit 20 may be a vessel having one or more agitation features such as a grinder, an impeller, a sonication unit, or the like. The slurry preparation unit 20, in a general sense, mixes the solid fuel 14, the liquid 16, and the organic compound 18 to generate a fuel slurry 24.

The fuel slurry 24 is a mixture including at least the solid fuel 14, the liquid 16, and the organic compound 18. The solid fuel 14 may include a variety of carbonaceous fuels, such as coal, or another hydrocarbon source. In some embodiments, the solid fuel 14 may be sub-bituminous (low rank) coal, which contains a certain amount of inherent liquid (e.g., water) present in the solid fuel 14. Because of the higher moisture content of low rank coal, such solid fuels 14 may have a lower solids concentration (e.g., a lower concentration of actual coal) than other solid fuels (e.g., bituminous coal). The organic compound 18 of the fuel slurry 24 may include methanol, ethanol, or another suitable organic compound, or combination of organic compounds, that is miscible with the liquid 16 (e.g., water). The organic compound 18 may replace a portion of the liquid 16 that would otherwise be used to generate the fuel slurry 24. As described below, the organic compound 18 may be recycled from other components or processes in the system 10. However, in some embodiments, at least a portion of the organic compound 18 may be provided from an outside source. In some embodiments, the organic compound 18 may be entirely provided via the outside source.

Using the organic compound 18 to mix the fuel slurry 24 may increase the efficiency of the milling or grinding process used to break up the solid fuel 14 during slurry preparation. That is, it may take less energy to break up the solid fuel 14 when using a mixture of the organic compound 18 and the liquid 16 as compared to using the liquid 16 alone. In general, the liquid 16 is provided to the milling/grinding process to reduce dust accumulation in particles of the solid fuel 14 and to increase a rate of solid particle comminution. This refers to the rate at which a grinder (or mill) breaks up the solid fuel 14. During this grinding process, the liquid 16 wets the external surface of the solid particles and penetrates into cracks in the solid particles, thereby modifying the surface energy that supplements the mechanical energy of the grinder impacting the particles. Accordingly, compounds having a lower surface tension are able to penetrate further into cracks in particles of the solid fuel 14. In addition, compounds having a lower viscosity are better able to flow between solid particles, thereby wetting more outside surfaces of the particles. The organic compound 18 may have a lower surface tension and lower viscosity than the liquid 16. For example, at approximately 20° C., the surface tension of methanol (i.e., organic compound 18) is approximately 22.7 mN/m², while the surface tension of water (i.e., liquid 16) is approximately 72.8 mN/m². Similarly, at approximately 20° C., the viscosity of methanol is approximately 0.59 cP, while the viscosity of water is approximately 1 cP. In addition, the organic compound 18 may be more effective than the liquid 16 at wetting hydrophobic particles. Such is the case with coal, which contains significant amounts of carbon and hydrocarbons that slow down the wetting process when only water is used. As a result, it may take less energy for the slurry preparation unit 20 to break up the solid fuel 14 in a mixture of the organic compound 18 and the liquid 16 because of the faster wetting, increased pore penetration, and lower viscosity of the mixture. This may enhance the efficiency of the milling process to produce stable suspensions of coal particles in the fuel slurry 24.

After the fuel slurry 24 has been prepared within a desired concentration range, the system 10 directs the fuel slurry 24 to a gasifier 26. The gasifier 26 is configured to subject the fuel slurry 24 to gasification conditions. As a result of being subjected to these conditions, the solid fuel within the fuel slurry stream 24 reacts with oxygen (O₂) and water (H₂O) to generate syngas 28. In a general sense, the amount of syngas 28 that is produced is limited by, among other things, the size of the gasifier 26 as well as the amount of solid fuel 14 that enters the gasifier 26. More specifically, a higher concentration of the solid fuel 14 in the fuel slurry 24 means a higher energy content of the fuel slurry 24, leading to increased carbon conversion and a higher quality of the syngas 28 generated from the gasifier 26.

As noted above, because the solid fuel 14 is provided to the gasifier 26 as a part of the fuel slurry 24, it may be desirable to maximize the amount of solid fuel 14 contained within the fuel slurry 24. The amount of solid fuel 14 contained within the fuel slurry 24 may be considered to be a solids concentration of the fuel slurry 24 and is generally represented as a percentage (e.g., by weight). The solids concentration of the fuel slurry 24 may be advantageously increased by mixing the solid fuel 14 with the organic compound 18 as well as the liquid 16. To achieve a desired solids concentration, the fuel slurry 24 may include the solid fuel 14, liquid 16, and organic compound 18 combined in prescribed ratios. For example, the organic compound 18 may be included to replace a portion of the liquid 16, this portion being within a range of approximately 1-99%, 5-75%, 10-50%, 15-40%, or above approximately 5%. Such an addition of the organic compound 18 may lead to an increase of approximately 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or more of the solids concentration (e.g., weight percentage of the solid fuel 14 in the total fuel slurry 24). An increase in 2-3% of the solids concentration may provide noticeable improvements in the carbon conversion taking place during gasification, because of the additional amount of carbon and oxygen available for partial combustion.

The improvement in solids concentration may be especially noticeable when the solid fuel 14 used in the fuel slurry 24 is low rank coal. For example, in one embodiment, the solids concentration of the fuel slurry 24 generated by mixing low rank coal with just the liquid 16 is approximately 50%. When the organic compound 18 is added to replace approximately 5% of the liquid 16, the solids concentration of the mixture may increase to above approximately 60%, which is within a typical solids concentration range of bituminous coal. Therefore, it is possible to generate approximately the same amount of syngas 28 from a fuel slurry using low rank coal, mixed with the liquid 16 and the organic compound 18, as is possible with a fuel slurry using higher rank coal and only the liquid 16. The addition of the organic compound 18 may enable the system 10 to produce a relatively stable amount and quality of the syngas 28, even while using a variety of different fuel sources.

The system 10 may include an organic compound production unit 30 for generating the organic compound 18 from a portion of the syngas 28 produced by the gasifier 26. In this way, at least a portion of the organic compound 18 used to increase the concentration of the fuel slurry 24 is recycled by the system 10. As a result, the system 10 may efficiently increase the milling rate and the solids concentration of the fuel slurry 24.

FIG. 2 illustrates an embodiment of the system 10 including multiple sections and control components that may be present in the feedstock preparation unit 12 and/or the slurry preparation unit 20 of FIG. 1. In the illustrated embodiment, these sections include a storage unit 50, a grinder 52, a slurry tank 54, and the organic compound production unit 30. A controller 56 may control the operation of these and other sections of the system 10, as described below.

The grinder 52 is designed to produce the fuel slurry 24 by mixing the solid fuel 14 with the liquid 16 and the organic compound 18. The illustrated grinder is not limited to a single piece of machinery used specifically in grinding applications. Indeed, the grinder 52 may represent one or more mixing vessels of the feedstock preparation unit 12 and/or the slurry preparation unit 20 that mixes the solids fuel 14, liquid 16, and organic compound 18 to generate the fuel slurry 24. Again, such mixing vessels may include a grinder, a mill, an impeller, a sonication unit, or any other agitation features generally used for mixing. Similarly, the grinder 52 may include multiple grinders in series used to prepare the fuel slurry 24 from its constituent components.

The storage unit 50 is designed to store the organic compound 18 and supply the organic compound 18 to the grinder 52 for mixing the fuel slurry 24. Upon generating the fuel slurry 24, the grinder 52 may provide the fuel slurry 24 to the slurry tank 54. The slurry tank 54 is a vessel located between the grinder 52 and the gasifier 26 used to store the fuel slurry 24 under a desired pressure. That is, the slurry tank 54 may include a pressurized chamber 58 for containing the fuel slurry 24. The pressurized chamber 58 may be a pressure vessel or negative pressure room (e.g., vacuum chamber). Enclosing the fuel slurry 24 in the pressurized chamber 58 may keep the slurry tank 54 from releasing undesirable vapor emissions from the organic compound 18 (e.g., methanol) to an outside atmosphere. In addition, the pressurized chamber 58 may separate the fuel slurry 24 from oxygen in the outside atmosphere, so that it does not react or otherwise interact with oxygen before reaching the gasifier 26. In some embodiments, there is no slurry tank between the grinder 52 and the gasifier 26, while in others there may be multiple such slurry tanks 54 and other pressurized vessels for conveying the fuel slurry 24 to the gasifier 26.

The gasifier 26 receives the fuel slurry 24 via a fuel injector and facilitates a combustion reaction between the fuel slurry 24, oxygen, and steam to generate the syngas 28. The syngas 28 may flow to a downstream system 60 for further processing. The downstream system 60 may include a gas treatment unit used to cool, clean, and otherwise prepare the syngas 28 for input to a downstream process, power generation system, or chemical production system. At least a portion of the syngas 28 flows to the organic compound production unit 30 for producing (e.g., via a once-through catalytic reaction) the organic compound 18 for supply to the slurry preparation unit 20 (e.g., the storage unit 50 and/or the grinder 52). In the illustrated embodiment, the organic compound production unit 30 receives a slipstream 62 of the syngas 28 that would otherwise be sent to the downstream system 60. In certain embodiments, however, the organic compound production unit 30 may be part of the downstream system 60. For example, a downstream chemical production system may send off-specification methanol (or another organic compound 18) to the slurry preparation unit 20. Off-specification methanol refers to methanol that is generated from the downstream chemical production system but cannot be used by the downstream chemical production system, because it does not meet certain requirements. This may be useful during startup or shutdown of the gasifier 26, when the gasifier 26 is not generating a consistent amount of the syngas 28. In addition, using the off-specification methanol may improve efficiency of the overall slurry preparation process, since the methanol would otherwise go unused. In some embodiments, the syngas 28 may be cleaned or otherwise treated prior to entering the organic compound production unit 30, or cleaned as a first step before a reaction takes place to produce the organic compound 18. In other embodiments, the slipstream 62 of syngas 28 may be dirty syngas exiting the gasifier 26. The organic compound 18 may be sent from the organic compound production unit 30 to the slurry preparation unit 20 in its raw form.

The controller 56 is configured to monitor and control the operation of the entire system 10, or components of the system 10, through signal lines 64 (e.g., feedback lines) and control lines 66. In some embodiments, one or more sensors 68 may transmit feedback from components of the system 10 to the controller 56 through the signal lines 64. The sensors 68 may detect or measure a variety of system and solids flow properties. The sensors 68 may include but are not limited to flow sensors, pressure sensors, position sensors, or torque sensors, or combinations thereof. The controller 56 may include a memory 70 and a processor 72. The memory 70, which may be any non-transitory, machine-readable medium, is configured to store machine-readable instructions that may be executed by the processor 72. These instructions may include various monitoring and control functions performed between the controller 56 and the system 10. For example, the controller 56 may process signals received from one or more of the sensors 68 to monitor a solids concentration, viscosity, pumpability, pore penetration, temperature, or other parameter of the fuel slurry 24 provided to the gasifier 26.

The controller 56 may control operation of the components of the system 10 by controlling actuators (e.g., valves) throughout the system 10. For example, the controller 56 may operate valves 74, 76, 78, 80, 81, 82, and 84 to control flows between the different system components. In addition, the controller 56 may govern operation of the gasifier 26 (e.g., ignition, supply of fuel, purging after gasifier shutdown, etc.) and the downstream system 60.

In the illustrated embodiment, the controller 56 governs operation of the first and second valves 74 and 76 to adjust a flow of the organic compound 18 from the organic compound production unit 30 to the grinder 52 and the storage unit 50, respectively. The controller 56 may control the third valve 78 to adjust a flow of the organic compound 18 from the storage unit 50 to the grinder 52. The first, second and third valves 74, 76, and 78 may be positioned based on an operational state of the gasifier 26. For example, the third valve 78 may be opened to supply the organic compound 18 to the grinder during gasifier startup and closed to stop the supply of the organic compound 18 during gasifier shutdown. In some embodiments, the first and second valves 74 and 76 may be positioned to supply the organic compound 18 from the organic compound production unit 30 to the grinder 52 during gasifier operation and to the storage unit 50 during gasifier shutdown. In other embodiments, the first and second valves 74 and 76 may be positioned to supply the organic compound 18 from the organic compound production unit 30 to the storage unit 50 during both operation and shutdown of the gasifier 26.

The controller may control an amount of the liquid 16 supplied to the grinder 52 via the fourth valve 80, and an amount of the solid fuel 14 supplied to the grinder 52 via the fifth valve 81. The controller 56 is able to control (via valves 74, 76, 78, 80, and 81) relative amounts of the organic compound 18, the liquid 16, and the solid fuel 14 sent to the grinder 52 for mixing the fuel slurry 24. The controller 56 may determine the desired relative amounts based on signals indicative of an operational state (e.g., startup mode, steady state mode, or shutdown mode) of the gasifier 26 and/or properties (e.g., viscosity, pumpability, flow velocity, pore penetration, solids concentration, or similar measurements) of the fuel slurry 24. In addition, the controller 56 may control the relative amounts of the syngas 28 flowing to the organic compound production unit 30 and to the downstream system 60 by adjusting a position of the sixth and seventh valves 82 and 84, respectively. There may be additional valves throughout the system 10 used to adjust different flows between system components.

In addition to mixing different relative quantities of the solid fuel 14, the liquid 16, and the organic compound 18, the system 10 may be able to mix these compounds in a prescribed sequence. For example, the system 10 may mix the organic compound 18 with the solid fuel 14 before introducing the liquid 16. This may be particularly useful when the solid fuel 14 is low rank coal, because the organic compound 18 can remove and/or replace (e.g., displace) an amount of water already present within the solid fuel 14 before the additional liquid 16 is added. In other embodiments, the system 10 may mix the liquid 16 with the solid fuel 14 (e.g., via the feedstock preparation unit 12) before introducing the organic compound 18. The controller 56 may control such sequenced mixtures of the solid fuel 14, the organic compound 18, and the liquid 16 by opening the valves 74, 78, and 80 at different relative times. In some embodiments, the grinder 52 may be equipped to provide such sequenced mixing of the fuel slurry 24. For example, FIG. 3 illustrates one such grinder 52, which may be considered to be two grinders 100 and 102 connected in series. The first grinder 100 (or first stage) may receive the organic compound 18 from the storage unit 50 and/or the organic compound production unit 30 and the solid fuel 14 to produce a solid fuel/organic compound mixture. This mixture is sent to the second grinder 102 (or second stage), where it is mixed with the liquid 16 to produce the final fuel slurry 24.

Present embodiments of the system 10 generate the fuel slurry 24 using the organic compound 18 that is at least partially recycled from other system components (e.g., syngas 28 from the gasifier 26). During an initial startup of the gasifier 26, however, there may be no syngas 28 readily available for producing the organic compound 18 used to mix the fuel slurry 24. Accordingly, when the gasifier 26 is starting up, the grinder 52 may receive the organic compound 18 from the storage unit 50. In certain embodiments, the organic compound 18 in the storage unit 50 is supplied by a source outside the system 10, such as a chemical production plant or other source of organic compounds. In other embodiments, the organic compound 18 in the storage unit 50 is supplied by the organic compound production unit 30 from the syngas 28 generated during a previous gasification reaction using the same gasifier 26. In another embodiment, illustrated in FIG. 4, an embodiment of the system 10 includes multiple gasifiers 26 that may provide the syngas 28 for production of the organic compound 18 and/or the generation of power, natural gas, or other compounds, or a combination thereof.

The system 10 illustrated in FIG. 4 includes three gasifiers 26 that may be used to provide the syngas 28 to the downstream system 60. In other embodiments, there may be different numbers of gasifiers 26, and the downstream system 60 may represent multiple systems and components configured to utilize the syngas 28 generated by the gasifiers 26. Each gasifier 26 may receive the fuel slurry 24 from an upstream system 110. As illustrated, each upstream system 110 may include the feedstock preparation unit 12 and the slurry preparation unit 20 to prepare the fuel slurry 24 from the fuel 14, liquid 16, and organic compound 18. The organic compound production unit 30 may receive syngas 28 from one or more of the gasifiers 26 to produce the organic compound 18 used to generate the fuel slurry 24 for one of the gasifiers 26. More specifically, the organic compound production unit 30 may receive a portion of the syngas 28 generated from one gasifier 26 to generate the organic compound 18 for supply to the upstream system 110 (e.g., storage unit 50) of another gasifier 26.

The controller 56 may monitor, among other things, the operational state of the gasifiers 26 to determine which gasifiers 26 are generating syngas 28. Based on the monitored operational states, the controller 56 may adjust valves 112 to control a flow of the syngas 28 from the gasifiers 26 to the downstream system 60 and/or to the organic compound production unit 30. These valves 112 represent, for each gasifier 26, the valves 82 and 84 shown in FIG. 2. The illustrated arrangement of the system 10 may enable any of the upstream systems 110 to receive the organic compound 18 produced from syngas 28 output by any operating gasifier 26. That is, during startup of one of the gasifiers 26, the corresponding upstream system 110 may generate the fuel slurry 24 using the organic compound 18. The organic compound 18 may be produced using the syngas 28 generated by another gasifier 26. The controller 56 may adjust the valves 112 such that more of the syngas 28 generated by one or more of the gasifiers 26 is sent to the organic compound production unit 30 during startup of another gasifier 26. Alternatively, the organic compound 18 may be provided from another of the storage units.

Having described various systems 10 for preparing the fuel slurry 24 using the organic compound 18, a more detailed discussion of embodiments of methods for operating and controlling such systems 10 will be provided. Certain of the methods for controlling the slurry preparation features described herein may be performed by the controller 56, which may be an application-specific or a general-purpose computer having the memory 70, processor 72, a data-accessing drive, and so on. The controller 56 may be configured to execute certain routines, for example after accessing the routines on a machine-readable, non-transitory medium such as an optical disc, solid state memory, or the like. Alternatively or additionally, the controller 56 may be connected to a distributed control system and/or a network, and may access the routines from a remote storage location. The controller 56 may thereafter execute the routines to facilitate the slurry preparation processes described herein. Non-limiting examples of embodiments of such control processes are described below with respect to FIGS. 5-8.

Keeping in mind that the methods set forth with respect to FIGS. 5-8 may be initiated or totally performed by the controller 56 as described above, FIG. 5 is a process flow diagram illustrating an embodiment of a method 130 for preparing the fuel slurry 24. Steps of the method 130 may be performed in other sequences and are not limited to any particular order, including the order provided in the illustrated embodiment. However, as described above, certain orders may be desirable. The method 130 may include starting (block 132) the gasifier 26, e.g., by introducing flows of fuel, steam, and/or oxygen to the gasifier 26 via a fuel injector or nozzle. The method 130 includes providing (block 134) the organic compound 18 to the grinder 52. As illustrated in FIG. 2, the organic compound 18 may be provided to the grinder 52 from the storage unit 50 and/or from the organic compound production unit 30. The method 130 also includes mixing (blocks 136 and 138) the organic compound 18 with the solid fuel 14 and the liquid 16 to generate the fuel slurry 24 via the grinder 52. In an embodiment, the fuel slurry 24 may be generated in a single step by mixing the solid fuel 14, the liquid 16, and the organic compound 18 together at once. In other embodiments, the steps may be sequenced. That is, the method 130 may include mixing (block 136) the organic compound 18 with the solid fuel 14 via the grinder 52 to generate an organic compound/solids mixture, and then mixing (block 138) the organic compound/solids mixture with the liquid 16 via the grinder 52 to generate the fuel slurry 24. In other embodiments, the sequence may be reversed, such that the method 130 includes mixing the organic compound 18 with the liquid 16 first to generate an organic compound/liquid mixture, and then mixing the organic compound/liquid mixture with the solid fuel 14 via the grinder 52. In still other embodiments, the steps of blocks 136 and 138 may be combined, such that the organic compound 18 is mixed with both the solid fuel 14 and the liquid 16 via the grinder 52. In such embodiments, the solid fuel 14 may already be mixed with the liquid 16 prior to the addition of the organic compound 18.

The method 130 further includes generating (block 140) the syngas 28 from the organic compound 18/solid fuel 14/liquid 16 mixture (i.e., fuel slurry 24) via the gasifier 26. The method 130 also includes generating (block 142) an additional amount of the organic compound 18 from the syngas 28 (e.g., via the organic compound production unit 30). Further, the method 130 includes providing (block 144) the additional amount of the organic compound 18 to the storage unit 50 (e.g., block 146), to the grinder 52 (e.g., block 134), or both. The system component to which the additional amount of the organic compound 18 is provided may depend on the particular system 10 and an operational state of the gasifier 26.

The additional organic compound 18 produced from the syngas 28 may be provided (block 146) to the storage unit 50 and not to the grinder 52 when the gasifier 26 is not operating. This may be implemented in the system 10 of FIG. 2 by the controller 56 closing the valves 74 and 78, thereby stopping the organic compound 18 from flowing into the grinder 52. Since the gasifier 26 is not operating, there is no demand for the fuel slurry 24 from the grinder 52.

During gasification, some embodiments of the system 10 may provide (block 134) the additional amount of the organic compound 18 to the grinder 52 and not to the storage unit 50. This may be accomplished by the controller 56 of FIG. 2 closing the valve 76 and opening the valve 74 when the gasifier 26 is operating. This may be useful for providing the organic compound 18 to the grinder 52, while maintaining a supply of the organic compound 18 in the storage unit 50 for later use. When the gasifier 26 is started up again, the organic compound 18 in the storage unit 50 may be utilized to generate the fuel slurry 24 for starting the gasification reaction.

Other embodiments, during gasification, may provide (blocks 134 and 146) the additional amount of the organic compound 18 to both the grinder 52 and to the storage unit 50. This may allow the organic compound 18 to flow to the grinder 52 for generating the fuel slurry 24 and to the storage unit 50 for building up a supply of the organic compound 18 for use during gasifier startup. In the system 10 of FIG. 2, this may be accomplished in different ways. First, the controller 56 may open the valves 74 and 76, but close the valve 78. Second, the controller 56 may open the valves 76 and 78, and close the valve 74. This may enable the organic compound 18 produced by the organic compound production unit 30 to flow into the storage unit 50 and from the storage unit 50 into the grinder 52. Third, all three of the valves 74, 76, and 78 may be opened. The controller 56 may adjust positions of these valves so that a desired total amount of the organic compound 18 flows into the grinder 52 and a desired amount of the organic compound 18 remains in the storage unit 50.

FIG. 6 is a process flow diagram illustrating an embodiment of a method 150 for controlling the system 10. The method 150 includes monitoring (block 152) a solids concentration of the fuel slurry 24. The solids concentration may be monitored directly or indirectly via one or a combination of sensors 68 located throughout the system 10. Indirect monitoring of the solids concentration involves monitoring, via the sensors 68, one or more parameters indicative of the weight percentage of the solid fuel 14 present in the generated fuel slurry 24. For example, the solids concentration may be indirectly measured based on a viscosity of the slurry, a temperature of the slurry, the power consumption by one or more slurry pumps, and the like.

The method 150 also includes controlling (block 154) an amount of the organic compound 18 supplied to the mixture (i.e., fuel slurry 24) based on the monitored solids concentration. Again, this organic compound 18 is at least partially recycled from the syngas 28 generated from the fuel slurry 24 via the gasifier 26. The amount of organic compound 18 provided to the grinder 52 may be controlled based on a number of factors including but not limited to a desired pore penetration of the solid fuel 14, a desired viscosity of the fuel slurry 24, or a desired temperature of the fuel slurry 24. For example, the temperature, the viscosity, or similar factors may limit the solids concentration suitable for certain applications. The pore penetration of the solid fuel 14 affects milling efficiency of the grinder 52, while the viscosity affects the pumpability of the fuel slurry 24 (e.g., through a fuel injector of the gasifier 26).

FIG. 7 is a process flow diagram illustrating an embodiment of a method 156 for performing the control step 154 of FIG. 6. The method 156 includes controlling (block 158) an amount of the organic compound 18 provided from the storage unit 50 to generate the fuel slurry 24. This may result in the grinder 52 receiving the organic compound 18 from the storage unit 50 during gasifier startup, prior to the gasifier 26 producing syngas 28 from which an additional amount of the organic compound 18 may be produced. By way of example, with reference to FIG. 2, this may include adjusting a position of the valve 78 to provide more or less of the organic compound 18 from the storage unit 50 to the grinder 52.

The method 156 also includes controlling (block 160) an additional amount of the organic compound 18 provided from the organic compound production unit 30 to generate the mixture (i.e., fuel slurry 24). As discussed above, the organic compound production unit 30 may produce this additional amount of the organic compound 18 from a portion of the generated syngas 28. The controller 56, for example, may execute this control step by adjusting a position of valve 74.

FIG. 8 is a process flow diagram illustrating an embodiment of a method 162 for controlling the system 10 during a transition from gasifier operation to gasifier shutdown. During gasifier operation (e.g., a steady state mode), the method 162 includes controlling (block 154) the amount of organic compound 18 supplied to the mixture, as described above with reference to FIGS. 6 and 7. The method 162 also includes determining (block 164) whether the gasifier 26 is operating. This determination may be based on sensor feedback from the gasifier 26. If the gasifier 26 is still operating, the controller 56 controls the supply of the organic compound 18 as before. When the gasifier 26 is shut down, however, the method 162 includes stopping (block 166) a flow of the organic compound 18 from the storage unit 50 (e.g., by closing the valve 78 of FIG. 2) to the grinder 52 for generating the fuel slurry 24. The grinder 52 may stop mixing the organic compound 18 with the solid fuel 14 and the liquid 16 at this point, since the fuel slurry 24 may not be used by the gasifier 26. However, it should be noted that in certain embodiments, the fuel slurry 24 may be generated according to the present technique even when the gasifier 26 is not operating. Indeed, it may be desirable to maintain a store of fuel slurry 24 so as to enable the gasifier 26 to be placed into operation nearly immediately.

The method 162 may further include refilling (block 168) the storage unit 50 with any additional amount of the organic compound 18 produced from the organic compound production unit 30. Although the gasifier 26 is not operating, the organic compound production unit 30 may still produce the organic compound 18 from the syngas 28 generated by the gasifier 26 just before shutdown. In the system 10 of FIG. 2, for example, the controller 56 may send control signals to close the valves 74 and 78, and to open the valve 76, thereby supplying the additional organic compound 18 to the storage unit 50. By refilling the storage unit 50 after gasifier operation, the system 10 may build up a store of the organic compound 18 for future use (e.g., during gasifier startup at a later time).

Technical effects of the present embodiments include, among other things, the ability to improve efficiency of fuel slurry preparation in a gasification system. Indeed, the use of an organic compound in generating a fuel slurry may enable an increase in the amount of carbon and oxygen available in the slurry for partial combustion in the gasifier. This may result in greater conversion of carbon within the gasifier to produce a syngas, as well as a lower oxygen demand on the gasifier. In addition, the organic compound may penetrate deeper into pores of the solid fuel compared to other compounds such as water, which modifies the surface energy to promote formation and propagation of cracks. As a result, the grinder or mill is able to break up the solid fuel using a reduced amount of energy, thereby increasing the milling rate and grinder efficiency. The organic compound also enables high solids concentrations compared to fuel slurries generated using fuel and water alone. Further, low rank coal and other fuel sources, which typically only generate low solids concentrations, may also be used to generate high solids concentrations (e.g., greater than approximately 60% by weight). Further, the organic compound may be recycled from a portion of the syngas generated by the gasifier. A controller may control the relative supply of solid fuel, liquid, and organic compound to achieve the desired solids concentration and viscosity of the fuel slurry, as well as pore penetration of the solid fuel. In addition, the controller may introduce the organic compound from different components (e.g., organic compound production unit, storage unit, etc.) to the grinder at different times throughout gasifier operation. This may allow the system to maintain a desired supply of recycled organic compound in storage for later use. In the ways listed above, the disclosed embodiments may provide increased control of the slurry preparation process as well as increased efficiency of the gasification system.

This written description uses examples to disclose the present embodiments, including the best mode, and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. 

1. A system, comprising: a grinder configured to produce a fuel slurry from a solid fuel, a liquid, and an organic compound that is miscible with the liquid; a storage unit configured to supply the organic compound to the grinder; and an organic compound production unit configured to receive a portion of syngas generated by a gasifier to generate the organic compound for supply to the storage unit.
 2. The system of claim 1, wherein the storage unit is configured to supply the organic compound to the grinder during startup of the gasifier.
 3. The system of claim 1, wherein the storage unit is configured to stop supplying the organic compound to the grinder during shutdown of the gasifier.
 4. The system of claim 3, wherein the organic compound production unit is configured to supply the organic compound to the grinder during operation of the gasifier, and to the storage unit during shutdown of the gasifier.
 5. The system of claim 3, wherein the organic compound production unit is configured to supply the organic compound to the storage unit during both operation and shutdown of the gasifier.
 6. The system of claim 1, comprising the gasifier configured to receive the fuel slurry and to generate the syngas from the fuel slurry.
 7. The system of claim 1, wherein the organic compound production unit is configured to receive a portion of syngas generated from another gasifier to generate the organic compound for supply to the storage unit.
 8. The system of claim 1, wherein the organic compound comprises methanol, ethanol, or a mixture of organic compounds having varying purity levels.
 9. The system of claim 1, comprising a controller configured to control an amount of the organic compound that is mixed with the solid fuel and the liquid in order to maintain a desired pore penetration of the solid fuel or viscosity of the fuel slurry in response to a monitored solids concentration of the fuel slurry.
 10. The system of claim 1, comprising a vessel disposed between the grinder and the gasifier, wherein the vessel is configured to store the fuel slurry under a desired pressure.
 11. A method, comprising: providing an organic compound from a storage unit to a grinder; mixing the organic compound with a solid fuel and a liquid to generate a fuel slurry via the grinder; generating an additional amount of the organic compound from a syngas, wherein the syngas is generated from the fuel slurry via a gasifier; and providing the additional amount of the organic compound to the grinder for mixing the fuel slurry or to the storage unit.
 12. The method of claim 11, comprising: starting the gasifier; and receiving and gasifying the fuel slurry to generate the syngas.
 13. The method of claim 11, comprising providing the additional organic compound to the storage unit and not to the grinder when the gasifier is not operating.
 14. The method of claim 13, comprising providing the additional amount of the organic compound to the grinder and not to the storage unit during gasification.
 15. The method of claim 13, comprising providing the additional amount of the organic compound to both the grinder and the storage unit during gasification.
 16. The method of claim 11, comprising supplying the organic compound to the storage unit from an outside source.
 17. The method of claim 11, comprising: mixing the organic compound with the solid fuel via the grinder to generate an organic compound/solids mixture; and mixing the organic compound/solids mixture with the liquid via the grinder to generate the fuel slurry.
 18. A system, comprising: a controller configured to: monitor a solids concentration of a fuel slurry comprising a mixture of a solid fuel, an organic compound, and a liquid; and control an amount of the organic compound supplied to the mixture based on the monitored solids concentration; wherein the organic compound is at least partially recycled from a syngas generated from the fuel slurry via a gasifier.
 19. The system of claim 18, wherein the controller is configured to: control an amount of the organic compound provided from a storage unit to generate the mixture; and control an additional amount of the organic compound provided from an organic compound production unit to generate the mixture, wherein the organic compound production unit is configured to produce the additional amount of the organic compound from a portion of the generated syngas.
 20. The system of claim 19, wherein the controller is configured to stop a flow of the organic compound from the storage unit to generate the mixture, and to refill the storage unit with the additional amount of the organic compound from the organic compound production unit when the gasifier is not operating. 